In recent years, a number of minimally invasive technologies have been developed for treating diseases, such as atherosclerosis, that result in narrowing of blood vessels, for example, within the coronary or carotid arteries. Tubular prostheses or “stents” have been developed for maintaining the patency of a blood vessel, for example, following angioplasty or other procedures used to treat a stenosis, occlusion, or other lesion within the blood vessel. The stent may be implanted across a treatment site to scaffold the site and prevent it from subsequently contracting or otherwise becoming obstructed.
Generally, the stent may be placed upon a catheter in a contracted condition, and the catheter advanced endoluminally to the treatment site until the stent is positioned across the stenosis. The stent may then be deployed and substantially anchored at the treatment site. The stent may be self-expanding, i.e., may be biased to expand to an enlarged condition upon release from the delivery catheter, thereby automatically substantially anchoring the stent at the treatment site. Alternatively, the stent may be plastically deformable, i.e., may be expanded with the aid of a balloon, which may underlie the stent on the catheter. The balloon may be inflated to expand the stent from the contracted condition to the enlarged condition wherein the stent substantially engages the wall of the treatment site. A balloon, for example, on a separate balloon catheter, may also be used to further expand and/or anchor a self-expanding stent.
Similarly, for ablation procedures and the like, a catheter including an array of electrodes, for example, on an expandable basket assembly, may be provided. The device may be introduced into a body lumen, e.g., through the patient's vasculature into the heart, to treat conditions, such as heart arrhythmia.
With any of these devices, a sheath may be provided over the catheter to protect the elements on the distal end of the catheter, such as a stent, a balloon, and/or an array of electrodes. The sheath may be advanced distally over the proximal end of the catheter until it covers the distal end and the element(s) thereon, or the distal end of the catheter may be introduced into the sheath, and advanced until it is proximate the distal end of the sheath. The distal end of the catheter, with the overlying sheath thereon, may then be introduced into a patient and positioned at a treatment site, whereupon the sheath may be retracted to expose the distal end of the catheter. After treatment, the sheath may be advanced back over the distal end of the catheter, and the entire device withdrawn from the patient.
One of the problems associated with these devices is that they may have substantially blunt distal ends that may scrape along the wall of a vessel during advancement therethrough, possibly damaging the wall and/or dislodging embolic material from the wall. To facilitate atraumatic advancement, particularly through tortuous anatomy, transition tips have been suggested for these devices.
For example, a conical or tapered nosepiece may be provided on the distal end of the catheter. A sheath may be disposed over the catheter, for example, to substantially cover the stent or other underlying element, such that the nosepiece extends distally from the end of the sheath, a distal edge of the sheath abutting the nosepiece. The nosepiece may facilitate advancement of the device through a narrow region of a blood vessel, although it may also risk catching on the wall of the vessel and/or dislodging embolic material, e.g., between the distal edge of the sheath and the nosepiece. Following delivery of a stent from the device, the nosepiece is generally positioned distal to the treated lesion. If the nosepiece is withdrawn directly, the proximal edge of the nosepiece may catch on the stent struts, resulting in the potential for trauma and embolic debris release. Alternatively, the sheath may be re-advanced across the treatment site to “recapture” the nosepiece, although in this approach the distal edge of the sheath may also catch on the stent struts.
As an alternative to a tapered nosepiece, a sheath having a rounded distal end has been suggested, as disclosed in U.S. Pat. No. 5,593,412 issued to Martinez et al. Weakened areas or slits are provided in the distal end, thereby defining sections that may be softened upon introduction of warm saline solution. Once the sections are softened, the sheath may be retracted from an underlying balloon catheter to expose and implant a stent mounted on the catheter. Introduction of saline or other liquids into a patient's vasculature, however, may be undesirable, but is necessary in order to soften the sections on the distal end of the sheath and allow the stent to be deployed from the sheath.
Another problem associated with such delivery systems is that the sheaths and/or catheters may buckle during insertion, because of the distal force applied from the proximal end to advance them through the patient's vasculature. In addition, because of their tubular nature, they may kink when advanced through tortuous anatomy, possibly damaging the device or an element within the device.
Accordingly, it is believed that delivery systems that facilitate delivery of a stent through a patient's vasculature and/or that overcome the problems discussed above would be considered useful.